Semiconductor devices employing high resistivity in-based compound group III-IV epitaxial layer for current confinement

ABSTRACT

High resistivity In-based compound Group III-V epitaxial layers are used to prevent substantial current flow through a region of a semiconductor device, such as a CSBH, DCPBH, EMBH or CMBH laser, a LED, a photodiode, a HBT, or a FET. Also described is a hydride VPE process for making the high resistivity material doped with Fe. The Fe is supplied by a volatile halogenated Fe compound, and the extend of pyrolysis of the hydride is limited to allow transport of sufficient dopant to the growth area.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of application Ser. No.004,919 filed on Jan. 20, 1987 now abandoned, which, in turn, is acontinuation-in-part of application Ser. No. 621,071 filed on June 15,1984, now Pat. No. 4,660,208.

BACKGROUND OF THE INVENTION

This invention relates to semiconductor devices such as light emittingdevices, light detecting devices, light modulating devices, andtransistors, and to methods of making such devices.

A common problem in the fabrication of low threshold buriedheterostructure (BH) lasers in the InGaAsP/InP materials system is thecontrol of leakage currents (i.e., currents which bypass the activeregion of the device). These currents lead to high lasing threshold, lowdifferential quantum efficiency, abnormal temperature dependence ofthreshold current, and rollover of the lightcurrent (L-I)characteristic. All of these factors have a significant negative impacton the use of BH lasers in transmitters for fiber optic communicationsystems.

One possible solution to the problem of leakage current in buriedheterostructure lasers is the controlled introduction of highresistivity material into the device structure. This high resistivitymaterial could be used to block current flow through undesired leakagepaths. Previously, high resistivity liquid phase epitaxial (LPE) Al₀.65Ga₀.35 As (lightly Ge-doped) material has been utilized for currentconfinement in AlGaAs/GaAs buried heterostructure lasers, but subsequentattempts to produce high resistivity LPE InP material for this purposehave not been successful. Deuteron bombardment has also been shown toproduce highly resistive material from p-type InP, but this material isnot expected to remain highly resistive during subsequent processing. Inparticular, because the high resistivity is related to deuteron implantdamage, the resistivity anneals out at the high temperatures (e.g.,above about 600° C.) required for subsequent LPE growth.

In addition, bifurcated, reverse-biased p-n junctions have also beenreported for constraining current to flow through the active region ofInGaAsP/InP lasers. These blocking junctions have been fabricated by theimplantation of Be into n-InP substrates, by the diffusion of Cd inton-InP substrates, and by the epitaxial growth of a p-InP layer onto ann-InP substrate. But, all of these devices are impaired to some extentby leakage currents because of the imperfect blocking characteristics ofthe reverse-biased junctions.

More recently, D. P. Wilt et al. reported in Applied Physics Letters,Vol. 44, No. 3, p. 290 (February 1984) that InP/InGaAsP channelsubstrate buried heterostructure (CSBH) lasers with relatively lowleakage currents and low lasing thresholds can be fabricated byincorporating into the structure a high resistivity Fe-ion-implantedlayer which constrains pumping current to flow through the activeregion. The high resistivity layer is produced by an Fe-ion implant intoan n-type InP substrate followed by an annealing treatment prior to LPEgrowth. Although the resistivity of the Fe-ion-implanted layer is stableeven after being subjected to the high temperatures characteristic ofLPE growth, the thinness of the Fe-implanted layer (about 0.4 μm)renders it difficult to reproducibly position the thin active layer(about 0.1-0.2 μm thick) adjacent thereto. When the active layer is notso placed, shunt paths are created which allow leakage current to flowaround the active layer. In addition, the thinness of the Fe-implantedlayer permits a process known as double injection to create leakagecurrent directly through the Fe-implanted layer; that is, injection ofcarriers from the p-type and n-type layers which bound the thinFe-implanted layer produce undesirable current flow across it. Hence,high performance (low threshold, high efficiency) devices are hard tofabricate reproducibly.

SUMMARY OF THE INVENTION

In accordance with one aspect of our invention, a semiconductor deviceincludes a semiconductor body in which substantial current is preventedfrom flowing through a region of the body by including in the region anIn-based compound Group III-V epitaxial layer having the physicalcharacteristics (e.g., relatively high resistivity and large thickness)of an Fe-doped InP-based layer grown by metallo-organic chemical vapordeposition (MOCVD) or hydride vapor phase epitaxy (VPE). In oneembodiment, the device has an active region, and the layer has anopening through which current is constrained to flow to the activeregion.

Another aspect of our invention is a method of fabricating such devices,which includes an Fe-doped, In-based compound Group III-V semiconductorregion, comprising the steps of (1) forming a precursor gas comprising acarrier gas, a volatile dopant compound, a volatile indium compound, anda Group V hydride, (2) directing the precursor gas through a heatedchamber to contact a heated deposition body, and (3) inducing depositionof the compound semiconductor on the body, characterized in that thecarrier gas comprises an inert gas, the dopant compound includes iron,the concentration of hydrogen in the precursor gas is limited to preventexcessive precipitation of iron, and the concentrations of the volatileindium compound at the body and of the Group V hydride are maintainedsufficient to result in the desired deposition. In one embodiment of themethod the concentration of hydrogen is limited by controlling theamount of pyrolysis of the hydride.

In another embodiment of our invention, we have found that reproducibleBH lasers with low leakage currents, low lasing thresholds, excellenthigh frequency response and good reliability can be fabricated byincorporating into the structure a relatively thick, high resistivityFe-doped In-based epitaxial layer. This layer is preferably grown byMOCVD or hydride VPE but may also be grown by any of several otherepitaxial techniques including, for example, chemical beam epitaxy(CBE). Importantly, InP: Fe layers which are relatively thick (e.g., 1-4μm) and highly resistive (e.g., 10³ -10⁹ Ω-cm) are realized by theseprocesses, characteristics which are crucial to reducing leakagecurrents and increasing yields in a variety of devices. In this regard,the use of hydride VPE in accordance with the invention is particularlyadvantageous because the high resistivity InP: Fe can be reproduciblygrown adjacent to masked features (e.g., mesas) without experiencingeither growth on the mask itself or unusual crystalline artifacts (e.g.,protrusions) adjacent to the mask.

For example, using hydride VPE to grow high resistivity InP: Fe blockinglayers alongside the mesa of an InP/InGaAsP etched mesa buriedheterostructure (EMBH) distributed feedback (DFB) 1.3 μm laser, we haveachieved single mode operation, CW threshold currents of less than 10mA, and output powers up to 20 mW. With stripe contacts 6 μm wide, asmall signal bandwidth of more than 15 GHz was measured.

On the other hand, using MOCVD to grow a high resistivity InP: Fe layeron an InP substrate, InP/InGaAsP CSBH 1.3 μm and 1.5 μm lasers with CWthreshold currents as low as about 10 mA and 8 mA, respectively, at roomtemperature (23° C.) have been achieved in accordance with ourinvention. These devices also had excellent high frequency performanceas evidenced by a small signal bandwidth as high as 8 GHz and modulationrates as high as 2.0 Gb/s.

In a similar fashion, InP: Fe epitaxial layers may be utilized as thecurrent-blocking layers of a double channel planar buriedheterostructure (DCPBH) lasers and covered (or capped) mesa buriedheterostructure (CMBH) lasers as discussed hereinafter.

In addition, the invention is also suitable for use in LEDs,photodiodes, modulators, heterojunction bipolar transistors (HBTs),field effect transistors (FETs) and other In-based compound Group III-Vdevices in which substantial current is prevented from flowing through aregion of the device.

BRIEF DESCRIPTION OF THE DRAWING

Our invention, together with its various features and advantages, can bereadily understood from the following, more detailed description takenin conjunction with the accompanying drawing, in which, in the interestsof clarity, the figures have not been drawn to scale:

FIG. 1 is an isometric view of a CSBH light emitting device inaccordance with one embodiment of our invention;

FIG. 2 is an end view of another embodiment of a CSBH device inaccordance with our invention;

FIG. 3 is an end view of a DCPBH device in accordance with still anotherembodiment of our invention;

FIG. 4 is an end view of a re-entrant EMBH device in accordanced withyet another embodiment of our invention; and

FIG. 5 is an end view of a CMBH device in accordance with one moreembodiment of our invention.

DETAILED DESCRIPTION

The semiconductor light emitting device shown in FIG. 1 may be used as alaser or as an edge-emitting LED. In either case, the device 10 includesan active region 12 in which the recombination of electrons and holescauses radiation to be emitted at a wavelength characteristic of thebandgap of the semiconductor material of the active region (e.g., about1.0-1.65 μm for InGaAsP depending on the specific composition of thequaternary). The radiation is directed generally along axis 14 and isprimarily stimulated emission in the case of a laser and primarilyspontaneous emission in the case of an LED.

This recombination radiation is generated by forward-biasing a p-njunction which causes minority carriers to be injected into the activeregion. Source 16, illustratively depicted as a battery in series with acurrent-limiting resistor, supplies the forward bias voltage and, inaddition, provides pumping current at a level commensurate with thedesired optical output power. In a laser, the pumping current exceedsthe lasing current threshold.

In general, the device inlcudes means for constraining the pumpingcurrent to flow in a relatively narrow channel through the active region12. As illustrated, this constraining means comprises a bifurcated, highresistivity Fe-doped InP epitaxial layer 20, and the active region 12has the shape of a stripe which lies in the rectangular opening (topview) of the bifurcated layer 20. Note, in the case of a surfaceemitting LED the layer 20, rather than being bifurcated, might take theshape of an annulus surrounding a cylindrical or mesa-like activeregion.

The structure shown in FIG. 1 is known as a channel-substrate buriedheterostructure (CSBH) laser which includes an n-InP substrate 22 and anFe-doped high resistivity InP epitaxial layer 20 which is bifurcated bya groove 24. The groove is etched or otherwise formed through layer 20into substrate 22. A preferred technique for controllably etching thegroove in the shape of a V is described in U.S. Pat. No. 4,595,454granted to W. C. Dautremont-Smith and D. P. Wilt on June 17, 1986. Thatpatent is incorporated herein by reference.

Briefly, this etching technique entails the use of a composite etch maskcomprising a thin (e.g., 18-22 Å native oxide layer formed on a(100)-oriented InP surface and a SiO₂ layer plasma deposited on thenative oxide. The native oxide layer may be grown using plasma enhancedor thermal methods. The mask is patterned using standardphotolithography and plasma etching so that the mask openings (.sub.˜<2.2 μm wide) are parallel to the [011] direction. V-grooves that are3.0 μm deep with only (111)B-oriented sidewalls are formed by roomtemperature etching in HCl-rich etchants such as 3:1 HCl:H₃ PO₄.

The following essentially lattice-matched epitaxial layers are thengrown by LPE on the etched wafer: an n-InP first cladding layer 26 (thecentral portion of which fills at least the bottom portion of groove24); an unintentionally doped InGaAsP layer 28; a p-InP second claddinglayer 30; and a p-InGaAs (or p-InGaAsP) contact-facilitating layer 32.Layer 28 includes crescent-shaped active region 12 which, in practice,becomes separated from the remainder of layer 28 because epitaxialgrowth does not take place along the top edges of the groove 24.Provided that nonradiative recombination at the interface with highresistivity layer 20 is not significant, the active layer is preferablyvertically positioned within the thickness of the high resistivity layer20 in order to reduce leakage current. However, if the active layer isbelow layer 20, but near enough thereto (i.e., .sub.˜ <1 μm away),leakage currents are still significantly reduced and nonradiativerecombination at the layer 20 interface becomes much less of a problem.

Although the high resistivity InP: Fe layer 20 is formed directly on thesubstrate 22, it may also be formed on an epitaxial buffer layer (notshown) grown on the substrate. In either case, we have found that thehigh resistivity of layer 20 is advantageously achieved by the MOCVDprocess described by W. D. Johnston, Jr. and J. A. Long in U.S. Pat. No.4,716,130 issued on Dec. 29, 1987 based on a copending application whichis incorporated herein by reference.

Briefly, this MOCVD process involves the use of a ferrocene-based oriron pentacarbonyl-based dopant precursor (or a combination of suchprecursors) in conjunction with an indium-organic material such as anindium alkyl. Advantageously, trimethylindium is used as the source ofindium. Alternatively, an adduct may be formed first between theindium-organic and an alkyl phosphine. The adduct is introduced into thegas stream by a flowing gas (e.g., hydrogen or an inert gas) through abubbler containing it. A source of phosphorus (e.g., phosphine) is alsointroduced into the gas flow. The dopant precursor is introduced toyield a mole ratio of iron to indium in the gas stream in the range1.2×10⁻⁴ to 1×10⁻⁵.

Relatively thick (e.g., 1-4 μm) InP: Fe layers with resistivities ashigh as 1×10⁹ Ω-cm are achievable by this process which is alsoapplicable to other In-based compound Group III-V compositions (e.g.,InGaP, InAsP, InGaAsP, InGaAlP). For lasers, however, a resistivity inexcess of about 1×10⁶ Ω-cm is desirable.

Alternatively, the high resistivity Fe-doped In-based compound GroupIII-V epitaxial layer may be grown by hydride VPE. In the prior art thishas been a difficult task because suitable volatile iron compoundstypically cannot be transported using a H₂ carrier at temperaturesnormally used for growth (T.sub.˜ >650° C.); that is, the presence oftoo much H₂ will reduce the volatile Fe compound and may cause excessiveFe metal to be deposited on the walls of the reactor. On the other hand,the growth of InP in an inert carrier is difficult and has been reportedonly for a trichloride system (using PCl₃) when PH₃ was added tostimulate growth. See P. L. Giles et al., Journal of Crystal Growth,Vol. 61, p. 695 (1983). However, in accordance with one aspect of ourinvention an Fe-doped, In-based compound Group III-V semiconductorregion is formed by hydride VPE using an inert carrier gas (e.g., N₂, Aror He), a volatile compound including Fe (e.g., a halogenated Fecompound such as FeCl₂, FeBr₂, or FeOCl) and by preventing excessiveprecipitation of Fe metal (e.g., by limiting the pyrolysis of PH₃). Inone embodiment high resistivity InP: Fe is grown using N₂ as a carrierunder conditions of limited PH₃ pyrolysis in the reactor. By using aninert carrier and limiting the presence of H₂ to that formed by thereaction of HCl with In.sub.(l) and Fe.sub.(s) and the pyrolysis of PH₃,we have achieved transport of sufficient FeCl₂ to produce InP: Fe with aresistivity of about 5×10⁴ to 2×10⁸ Ω-cm. Resistivities lower than 5×10⁴are readily achieved, if so desired.

A high resistivity layer prepared by either the MOCVD or hydride VPEprocess described above maintains its high resistivity even after beingsubjected to the high temperatures of subsequent process steps.

Returning now to FIG. 1, electrical contact is made to the device viametal electrodes 34 and 36 on layer 32 and substrate 22, respectively.Source 16 is connected across electrodes 34 and 36.

Although a broad-area contact is depicted in FIG. 1 by layer 32 andelectrode 34, it also is possible to delineate a stripe geometry contactas shown in FIG. 2. Here components with primed notation in FIG. 2correspond to those with the same reference numerals in FIG. 1. Thus,the contact-facilitating layer 32' is etched to form a stripe and isaligned within the stripe-shaped opening of SiO₂ layer 33. Astripe-shaped metal contact 35 is formed on layer 32' in the opening ofSiO₂ layer 33, and a broad area electrode 34' is then formed over thetop of the device. A contact configuration of this type reduces devicecapacitance and hence increases high speed performance.

The CSBH laser also includes means for providing optical feedback of thestimulated emission, typically a pair of separated, parallel, cleavedfacets 38 and 40 which form an optical cavity resonator as shown inFIG. 1. The optical axis of the resonator and the elongated direction ofthe stripe-shaped active region 12 are generally parallel to oneanother. Other feedback techniques are also suitable, however, includingwell-known distributed feedback gratings, for example.

EXAMPLE I

The following example describes the fabrication of an InP/InGaAsP CSBHlaser in accordance with one embodiment of our invention. Unlessotherwise stated, various materials, dimensions, concentrations,operating parameters, etc., are given by way of illustration only andare not intended to limit the scope of the invention.

In this example we demonstrate for the first time the utilization of ahigh resistivity, Fe-doped InP layer grown by MOCVD as the basestructure for a InGaAsP/InP CSBH 1.3 μm laser. Pulsed threshold currentsas low as 11 mA and pulsed light output as high as 14 mW at 100 mA havebeen achieved for this structure, with good yield and uniformity ofdevices. The superior high frequency response expected for a device witha semi-insulating base structure has been verified, with small signalbandwidths exceeding 2.4 GHz. In addition, modulation at rates as highas 2.0 Gb/s has been achieved.

The CSBH lasers, of the type shown in FIG. 2, were fabricated asfollows. Using the MOCVD epitaxial reactor described in U.S. Pat. No.4,716,130 of W. D. Johnston, Jr. and J. A. Long, supra, a single layer20 of Fe-doped InP was grown on an n-type InP substrate 22 (S-doped LECmaterial) nominally oriented along the (100) plane (no intentionalmisorientation was employed).

The Fe-doped layer was between 1 and 4 μm thick and had a resistivity ofat least 1×10⁶ Ω-cm. Then a composite native oxide/SiO₂ etching mask wasdeposited as described in U.S. Pat. No. 4,595,454 of W. C.Dautremont-Smith and D. P. Wilt, supra. The mask was patterned into 2.0μm wide windows, and the V-groove 24 for subsequent LPE growth wasetched in a mixture of 3:1 HCl:H₃ PO₄. The mask was then stripped in HF,and the wafer was loaded into a LPE reactor. Prior to the LPE growth,the wafer was protected in an external chamber containing a saturatedSn-In-P solution as described by P. R. Besomi et al. in U.S. Pat. No.4,482,423 issued on Nov. 13, 1984, which is incorporated herein byreference. The DH (layers 26, 28 and 30) was then grown by LPE atapproximately 630° C. These layers included an n-type InP (Sn-doped)layer 26, a nominally undoped InGaAsP (λ_(g) ≈1.3 μm) layer 28, and ap-type InP (Zn-doped) layer 30. On the DH a contact-facilitating p-typeInGaAsP (λ_(g) ≈1.2 μm, Zn-doped) layer was grown and later etched asdescribed below. The width and thickness of the crescent-shaped activeregion 12 were typically 2.5 μm and 0.2 μm, respectively. Care was takento grow the active region in the channel and within the thickness of thehigh resistivity layer 20 in order to reduce leakage current and shuntcapacitance. However, even when the active layer was below layer 20, butwithin about 1 μm of it, the laser performance exceeded that of priordesigns (i.e., either those with Cd-diffused base structures or Fe-ionimplanted base structures).

After the LPE growth was completed, standard channel substrate buriedheterostructure laser processing was performed. First, SiO₂ wasdeposited over the surface of the wafer and patterned into stripesdirectly over the buried active regions, with the alignment performed byetching of the wafer edges to reveal the buried structure. The contactfacilitating layer of the structure was then etched in 10:1:1 H₂ SO₄ :H₂O₂ :H₂ O to leave InGaAsP stripes 32' as shown in FIG. 2, and the SiO₂etch mask was stripped in HF. Another SiO₂ layer 33 was then depositedand patterned to form windows over the stripes of layer 32'. Thephotoresist used in patterning the SiO₂ layer 33 was then used as aliftoff mask for an evaporated AuZnAu contact 35. After alloying theAuZnAu contact 35, the wafer (substrate) was lapped and a back (n-side)contact pad of AuGe was deposited and alloyed, using a similar liftofftechnique. A front (p-side) TiPt overlay metallization (not shown) wasdeposited and sintered, and both front and back sides of the wafer wereplated with Au layers 34' and 36 to serve as contacts and as bondingpads. Finally, the wafer was scribed and cleaved into individual chips250 μm long by 500 μm wide.

The pulsed light-current (L-I) and dL/dI characteristics of the laserswere measured. One laser had a threshold current at 30° C. of 21 mA andachieved 10 mW of output power at a current of 85 mA. The light outputat 100 mA was 11.8 mW. The peak slope efficiency was 0.18 mW/mA, equalto our best results on other lasers with good current confinement. Thepeak efficiency was maintained well throughout this range, droppingslightly at the higher power levels, possibly due to current flow aroundthe edges of the active region or current flow into regions of the layer28 not responsible for stimulated emission (e.g., the "wings" of thecrescent-shaped active region). The I dV/dI saturation for this devicewas measured to be near ideal at threshold, indicative of good currentconfinement.

The good intra-wafer uniformity available for this type of device wasillustrated by tight distributions in threshold current and light outputat 100 mA under pulsed conditions. For a random sample of 25 unbondeddevices from this wafer, the mean threshold current was 20.1 mA, themedian threshold current was 19.2 mA, and the standard deviation of thedistribution was 4.6 mA. The mean light output at 100 mA was 9.93 mW,the median was 11.4 mW, and the standard deviation was 1.8 mW.

The burn-in characteristics of a group of lasers with this structure,under 60° C. and 3 mW automatic power control burn-in conditions,illustrated their good stability. The degradation rates measured onbonded, purged lasers were as low as 1 mA per thousand hours at the 60°C.-3 mW burn-in conditions. Purging is described by E. I. Gordon et al.in U.S. Pat. No. 4,573,255 issued on Mar. 4, 1986. This degradation rateis low enough for these lasers to be used in optical communicationssystems.

The far field emission patterns were measured at 3 mW CW output power.The measured half power beamwidths were 17° and 28° parallel andperpendicular to the junction plane, respectively. An optical emissionspectrum exhibited a few longitudinal modes centered at a wavelength of1.2925 μm.

The modulation response of this laser was particularly good. Rise andfall times measured with a high speed driver were approximately 0.3 nsand high speed modulation was achieved at rates as high as 2 Gb/s withgood eye patterns. The small signal response was plotted as a functionof optical power output. The 3 dB cutoff frequency varied from 2.1 GHzat the lasting threshold to a maximum of more than 2.4 GHz at 1 mW ofoptical power. Thereafter, this cutoff frequency fell to 2.0 GHz at 2 mWand 1.8 GHz at 3 mW.

EXAMPLE II

Using procedures similar to those of Example I, we fabricatedInP/InGaAsP CSBH lasers operating at about 1.3 μm or 1.5 μm. The shorterwavelength lasers had CW room temperature thresholds of about 10 mA and3 dB cutoff frequencies as high as 8 GHz. The longer wavelength lasershad corresponding thresholds of 8 mA and are expected to have comparablecutoff frequencies.

EXAMPLE III

This example describes the fabrication of high resistivity InP: Feepitaxial layers by a hydride VPE process. As above, other In-basedcompound Group III-V materials (e.g., InGaP, InAsP, InGaAsP, InGaAlP)can also be made by this process. These high resistivity layers havebeen incorporated into EMBH and CNBH lasers of the type shown in FIGS. 4and 5, respectively, and can be used in other device structures as well.As before, the various materials, dimensions, concentrations, etc., aregiven by way of illustration only and are not intended to limit thescope of the invention unless otherwise stated.

The reactor used for the growth of the InP: Fe is described by R. F.Karlicek et al. in Journal of Applied Physics, Vol. 60, p. 794 (1986).Note, the reactor contains a quartz growth tube, and to grow Group III-Vcompounds containing Al, the interior walls of the tube should beprotected by a coating such as graphite. For the growth of InP: Fe thesource gases included HCl and PH₃ mixtures (5% and 2%, respectively) inultra high purity (99.999% pure) N₂ carrier gas which was obtainedeither from a standard compressed gas cylinder or from purified N₂boiloff from a liquid nitrogen tank. The concentration of the inputreactive gases was selected using electronic mass flow controllers. Thetransport of iron as the dichloride FeCl₂ was accomplished by flowingHCl (5% in N₂) through iron powder (99.999% pure) placed on a quartzfrit or by flowing HCl over crumpled iron foil (99.999% pure) placed ina separate tube. The outlet of the tube or the frit was locateddownstream of the In.sub.(l) source in the reactor source region. TheIn.sub.(l) source temperature, the Fe source temperature, and the growthtemperature were kept constant. The In and Fe source temperature was700° C. (a range of 700°-750° C. is suitable), and the growthtemperature was also 700° C. (a range of 650°-700° C. is suitable).Between growth experiments, Pd-purified H₂ was made to flow through thereactor in place of N₂.

Using an optical spectrometer which monitored the wavelength regionbetween 200 and 330 nm, the extent of PH₃ pyrolysis was determined bymeasuring the absorbance by P₄ at 230 nm. Since P₄ is the dominantspecies (except for unpyrolyzed PH₃), the concentration of P₂ was notmonitored optically and was not included in the computation of thedegree of PH₃ pyrolysis during growth. A suitable range of PH₃ pyrolysisis 17-65%. Above 65% the dynamics of the process produce either etchingor no epitaxial growth. Less than 17% is difficult to achieve becausePH₃ pyrolysis on the quartz growth tube at 650°-700° C. produces some H₂in the growth region. In general, we have achieved reproducible results,with the growth rate and surface morphology of the InP: Fe beingessentially independent of the degree of pyrolysis in the range of17-26%. The transport of FeCl₂ was also monitored optically, and theconcentration was computed from published thermodynamic data for theFe-Cl system.

The growth of InP: Fe was performed on <100> oriented InP: S substrateswhich were degreased prior to placement in the reactor. Growth was alsoperformed adjacent to mesas etched from epitaxial layers grown on thesubstrate. Following the preheating of the substrate under a dilute PH₃flow (e.g., 8×10⁻³ atm), a brief etch was performed by initiating theflow of HCl (e.g., 4×10⁻⁴ atm, no PH₃) through the Fe source. This etchis optional depending on the device being fabricated. Growth wasinitiated by starting the flow of HCl over the In.sub.(l) source region.The specific growth conditions were as follows: PH₃ pressure of17.9×10⁻³ atm (a range of 14-18×10³¹ 3 atm is suitable), InCl pressureof about 4.0×10⁻³ atm (not critical), HCl pressure over the Fe of1.0×10⁻⁴ atm (a range of 0.6-1.0×10⁻⁴ is suitable) and total flow of2250 sccm (2250-2300 is suitable). These conditions produced InP: Fegrowth rates of 16 μm/hr (12-20 μm/hr in the ranges indicated). Theresulting InP: Fe layer was measured to have a resistivity of about2.4×10⁸ Ω-cm (5×10⁴ -2.4×10⁸ in the ranges indicated). Theseresistivities have been obtained in n-type InP having a net carrierconcentration in the range of 5×10¹⁴ to 1×10¹⁶ cm⁻³.

It is to be understood that the above-described arrangements are merelyillustrative of the many possible specific embodiments which can bedevised to represent application of the principles of the invention.Numerous and varied other arrangements can be devised in accordance withthese principles by those skilled in the art without departing from thespirit and scope of the invention. In particular, other epitaxial growthtechniques may be suitable for growing high resistivity Fe-dopedIn-based compound Group III-V layers. Thus, chemical beam epitaxy (CBE)could be utilized with, for example, trimethyl indium, phosphine(cracked to yield P₂ and/or P₄) and ferrocene to provide sources of In,P and Fe respectively, in a H₂ stream. As with conventional molecularbeam epitaxy, growth takes place at low pressures in an ultrahigh vacuumchamber. In CBE the beams are generated by passing the gases throughappropriate nozzles, and the substrate (e.g., InP) is heated to thegrowth temperature.

Thus, the invention contemplates the ability to grow by a variety ofepitaxial techniques, In-based compound Group III-V epitaxial layershaving the physical characteristics (e.g., resistivities of .sub.˜ >10³Ω-cm and thicknesses of .sub.˜ >1 μm) of Fe-doped InP-based layers grownby either MOCVD or hydride VPE as described above.

In addition, while our invention has been discussed with reference tolasers and LEDs, it will be appreciated by those skilled in the art thatit is applicable to other semiconductor devices (e.g., photodiodes,modulators, HBTs, FETs) in which substantial current is prevented fromflowing through a region of the device. An example of a vertical InPFET, in which the gate is formed on the side wall of a V-groove throughan InP: Fe layer, is described by C. Cheng in copending application Ser.No. 896,772 filed on Aug. 15, 1986.

Other alternative device embodiments of our invention involve the DCPBH(FIG.3), EMBH (FIG.4) and CMBH (FIG. 5) configurations. The conventionalDCPBH laser is described generally by I. Mito et al. in Journal ofLightwave Technology, Vol. LT-1, No. 1, p. 195 (1983). It employs LPEregrowth in the channels to form reverse-biased blocking junctions whichconstrain current to flow through the elongated mesa containing theactive layer. In accordance with a DCPBH embodiment of our inventionshown in FIG. 3, however, the LPE regrowth of blocking junctions isreplaced by growth of InP: Fe zones 40 on each side of the mesa. Arestricted (e.g., stripe geometry) contact 42 is delineated on top ofthe mesa by a patterned dielectric layer 44 (e.g., SiO₂) and anelectrode 46 overlays the top of the device. In this fashion, current isconstrained by the InP: Fe zones 40 and the dielectric layer 44 to flowessentially only through the mesa and hence through the active layer 50.

A re-entrant EMBH laser is shown in FIG. 4. The active layer is locatednear the neck of the re-entrant mesa and high resistivity InP: Fe isgrown adjacent to the mesa to constrain current to flow primarilythrough the mesa and through the active layer. A similar EMBH (notshown) has vertical side walls. Lasers of both types have beenfabricated using the above-described hydride VPE process to grow theInP: Fe (hydride VPE can also be used to grow the other layers of thelaser as well). In both cases the lasers were of the DFB type, beingsupplied with a well-known first-order diffraction grating (not shown)in the substrate surface 60.

In a similar fashion, a CMBH-DFB laser of the type shown in FIG. 5 hasbeen fabricated with a grating on substrate surface 70. Although thistype of laser entails three epitaxial growth cycles, it has theadvantage that a shorter mesa is used which alleviates some of thedifficulty in etching the taller mesas of FIG. 4, for example.

The use of our hydride VPE technique to grow high resistivity blockinglayers adjacent to mesas (e.g., as in FIGS. 3-5) is preferred forseveral reasons: (1) growth does not occur on the mask (SiO₂ or SiN_(x))which remains on the mesa during epitaxial growth of the highresistivity material; (2) undesirable artifacts (e.g., protrusions)adjacent to the mask do not occur; (3) where the mesa is not masked, VPEcan be used to planarize the structure; and (4) the VPE process iscontrollable, being essentially unaffected to any significant extent bythe shape of the mesa or the size of the mask overhang.

Finally, it is well known that the active region of the devicesdescribed above may include a single active layer or a composite ofseveral layers at least one of which is active (in the light-emittingsense). Thus, in a 1.55 μm InP/InGaAsP laser, the active region mayinclude an InGaAsP layer which emits light at 1.55 μm adjacent anotherInGaAsP layer (λ=1.3 μm) which serves an anti-meltback function duringLPE growth. Moreover, several active layers emitting at differentwavelengths are also embraced within the definition of an active region.

What is claimed is:
 1. A semiconductor device comprisinga semiconductor body, means for applying current to said body, and means for preventing substantial current flow through a region of said body, characterized in that said preventing means comprises an In-based compound Group III-V epitaxial layer included in said region and having the physical characteristics of an Fe-doped InP-based MOCVD layer.
 2. The device of claim 1 wherein said layer has a thickness of .sub.˜ >1 μm.
 3. The device of claims 1 or 2 wherein said layer has a resistivity of .sub.˜ >10³ Ω-cm.
 4. A semiconductor device comprisinga semiconductor body, p1 means for applying current to said body, and means for preventing substantial current flow through a region of said body, characterized in that said preventing means comprises a high resistivity Fe-doped In-based compound Group III-V epitaxial layer included in said region.
 5. The device of claim 4 wherein said layer has a thickness of .sub.˜ >1 μm.
 6. The device of claims 4 or 5 wherein said layer has a resistivity of .sub.˜ >10³ Ω-cm.
 7. A semiconductor device comprisingan active region, electrode means for applying current to said device, and means for constraining said current to flow in a channel through said active region, characterized in that said constraining means comprises an In-based compound Group III-V epitaxial layer having an opening through which said channel extends and having the physical characteristics of an Fe-doped InP-based MOCVD layer.
 8. The device of claim 7 wherein said layer has a thickness of .sub.˜ >1 μm.
 9. The device of claims 7 or 8 wherein said layer has a resistivity of .sub.˜ >10³ Ω-cm.
 10. A semiconductor device comprisingan active region, electrode means for applying current to said device, and means for constraining said current to flow in a channel through said active region, characterized in that said constraining means comprises a high resistivity Fe-doped In-based compound Group III-V epitaxial layer having an opening through which said channel extends.
 11. The device of claim 10 wherein said layer has a thickness of .sub.˜ >1 μm.
 12. The device of claims 10 or 11 wherein said layer has a resistivity of .sub.˜ >10³ Ω-cm. 